A concrete product is produced via a process which involves kneading materials such as cement, aggregate, water and a dispersant (water-reducing agent), casting (filling) the resulting mixture into various forms and curing it. Realization of high strength in an initial material is important from the viewpoint of productivity (improvement in turnover of mold form), and for this purpose, measures are taken wherein for example, early-strength cement is used, various polycarboxylic acid compounds are used as an admixture to reduce the amount of water in cement compositions, and steam curing is carried out as a curing method. Because of desire for higher productivity, etc. at present, there may be demand for further reduction in the curing process, and realization of high strength (initial strength) in a curing period of 1 day or so may be required. Usually, complicated steps such as a step of heating with steam are incorporated into the curing process, but measures for improving initial strength by design changes in these steps serve hardly as practical means. From the viewpoint of production costs, etc., therefore, there is an earnest desire in the market for a method of obtaining concrete of high initial strength easily without involving changes in the process.
If voids and hollows considered attributable to insufficient filling are generated on the surface of a concrete product upon removal from a form (demolding) after the curing step and the texture of concrete surface is deteriorated due to other various factors, then the quality of the product is lowered. At present, concrete products having deteriorated surface texture are repaired manually after demolding. However, this operation requires many manpowers and much time and is thus regarded as one reason for increasing manufacturing costs. A variety of influencing factors on the surface texture of concrete products are known, among which (1) the amount and quality of voids generated during kneading, (2) the strength of concrete at the time of demolding and (3) concrete viscosity are said to be important factors.
Japanese Patent Application Laid-Open (JP-A) No. 2004-2175 proposes use of an admixture containing a polycarboxylic acid polymer and a polyhydric alcohol/alkylene oxide adduct to provide a cement composition with viscosity to facilitate operation. JP-A No. 2006-282414 discloses a strength enhancer for cement, which contains glycerin or a glycerin derivative and a specific polycarboxylic acid copolymer. JP-A No. 2001-294466 discloses an admixture for a hydraulic composition, which contains a specific shrinkage-reducing agent and a specific antifoaming agent. JP-A No. 2006-52381 discloses, as a high-performance water reducing agent, a phosphate polymer capable of producing low-viscosity concrete. JP-A No. 2007-77008 discloses a surface texture improver containing a specific amide compound and shows a specific polyoxyalkylene compound as a compound used in combination.